In recent years, in order to meet needs for space saving, assembility improvement, controllability improvement and the like of automobiles, there is an increasing tendency to change a mechanical drive system into a by-wire system, in which electrical driving is performed with a motor.
Such a by-wire system is described in, for example, Patent Document 1 (JP 2006-336691A). In Patent Document 1, based on predetermined monitor information, the by-wire system is monitored by a monitor control circuit, which is provided separately from a by-wire control circuit for controlling a motor serving as a drive source. When the monitor control circuit confirms an abnormality of the by-wire system, the control of the motor by the by-wire control circuit is prohibited (e.g., turning off a switch to prohibit the energization of the motor).
In the technology of Patent Document 1, the control of the motor is merely prohibited when the monitor control circuit confirms an abnormality of the by-wire system based on the predetermined monitor information. Thus, there is a possibility that it is difficult to sufficiently enhance safety in case of a system abnormality (e.g., generation of an abnormal signal due to noise, power supply voltage reduction or the like).
There is a system which includes a by-wire control circuit for driving rotation of a motor by sequentially switching the energized phase of the motor, and which switches the energized phase of the motor in a correct order in the following way. The by-wire control circuit pre-stores a table in which energized phases corresponding to respective energized phase pattern numbers are arranged in the correct order. When the by-wire control circuit drives the rotation of the motor, the by-wire control circuit refers to this table to determine the energized phase corresponding to the energized phase pattern number, thereby switching the energized phase of the motor in the correct order.
In such a system, in case that an abnormality sequentially incrementing the energized pattern number one-by-one occurs due to a RAM garbling (data garbling by RAM abnormality) or the like, there is a possibility that the abnormality switches the energized phase in the correct order of driving the rotation of the motor.